9s Remarks on the Nature of Sound in Water. 



which differs in a remarkable degree from its duration in air. 

 The sound of a bell struck under water, and heard at some dis- 

 tance, has no resemblance to that of a bell struck in the air. 

 Instead of a prolonged sound, there is only heard under water 

 a short and sharp noise, which I can compare to nothing bet- 

 ter than to that of two blades of knives struck against each 

 other. On retiring indefinitely from the bell, the sound always 

 preserves this character, only diminishing in intensity. The 

 perception of a sound so sharp and short coming from a distance 

 of several leagues, causes a feeling similar to that which one 

 experiences on seeing distant objects through a telescope with 

 the clearness which that instrument gives to them. In making 

 the experiment at intermediate distances, the sound always ap- 

 peared to me the same in nature, insomuch that I found it im- 

 possible to distinguish whether it came from a strong and distant 

 stroke, or a weak and near one. It is only at a distance of about 

 200 metres, that the ringing of the bell begins to be distinguish- 

 able after each stroke. In the air we observe a phenomenon al- 

 most entirely the reverse. The strokes applied to a bell are 

 more distinctly heard at hand, whereas at a distance there is 

 only heard a continued and almost uniform tingling. The re- 

 sistance which the water opposes to the vibrations of the bell, 

 does not afford a sufficient explanation of this fact, for the same 

 sound heard out of the water was much more prolonged ; the 

 sound of a bell was very well recognized, which would have been 

 impossible, in listening at a distance to the same noise transmitted 

 in water. This phenomenon is explained by the nature of the vi- 

 brations of sound in water. It is known, in fact, that, in the vibra- 

 tory motion of a fluid, the duration of agitation of a particle is 

 equal to the radius of the spherical portion of the fluid which is 

 originally shaken at the commencement of the motion, divided by 

 the velocity of transmission of the soimd. The first of these 

 two quahties is necessarily smaller in water than in air ; the 

 second, on the contrary, is greater ; whence it follows that the 

 duration of sound ought to be much less when it is transmitted 

 through water, than when propagated in the air. 



The second remark relates to the non-transmission of the sound 

 from ivater into air^ when the vibrations which are propagated 

 in the water arrive at its surface under a very small angle. Thus, 



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